1. Field of the Invention
The present invention relates to an improvement on a fluidic apparatus such as a pump, a compressor, or the like. For instance, when a fluidic apparatus according to the present invention is embodied as a variable capacity pump which starts up at substantially zero capacity, the variable capacity pump can be applied appropriately to a refrigerating circuit including a refrigerant compressor driven by a hydraulic motor, and thereby it effectively operates the refrigerant compressor by way of the hydraulic motor, and it can be also applied appropriately to hydraulic operation systems of vehicles equipped with special purpose machines, and thereby it effectively drives the special purpose machines.
2. Description of the Related Art
There have been axial piston pumps (hereinafter simply referred to as "pumps") which have been used in a variety of industrial machines and vehicles. FIG. 8 illustrates one of the conventional pumps, e.g., a variable capacity piston pump equipped with a mechanism adapted for adjusting the inclination angle of the swash plate.
In the conventional pump, there is formed an operating space 3 with a casing 1 and an end cover 2 which encloses an open end of the casing 1. A driving shaft 4 is disposed in the operating space 3, it is supported rotatably by the casing 1 and the end cover 2 by way of a pair of bearings 5, 5, and it is further connected to an input shutting-off mechanism (not shown) which comprises an electromagnetic clutch. A cylinder block 6 is disposed around the driving shaft 4, it is adapted to rotate together with the driving shaft 4 in the operating space 3, and it includes a plurality or, bores 7 disposed around the axial center line and parallel therewith. A plurality of pistons 10 are disposed reciprocatively in the bores 7, and they are installed to a swash plate 9 by way of shoes 8.
A valve plate 11 is fixed to the end cover 2 so as to enclose the open end of the bores 7, and it is provided with an inlet port 12a and an outlet port 12b. The ports 12a and 12b are drilled through the valve plate 11 in arc forms which oppose each other and correspond to the rotary locus of the openings of the bores 7, and they are formed so as to match ends of an inlet opening 13a and an outlet opening 13b. The inlet opening 13a and the outlet opening 13b are formed in identical forms with those of the ports 12a and 12b at the ends.
Thus, as the cylinder block 6 rotates together with the driving shaft 4, one of the pistons 10 installed to the swash plate 9 is reciprocated so as to increase the volume of the enclosed space in one of the bores 7, and accordingly the hydraulic oil is suctioned into one of the bores 7 through the inlet port 12a corresponding thereto. On the other hand, another one of the pistons 10 is reciprocated so as to decrease the volume of the enclosed space in another one of the bores 7, and accordingly the hydraulic oil is discharged from another one of the bores through the outlet port 12b corresponding thereto.
The swash plate 9 is supported by a trunnion type supporting shaft (not shown), and it is urged by a control spring 14 so as to always increase the inclination angle of the swash plate 9. A control cylinder 15 is disposed so as to oppose the control spring 14, and it is advanced or retracted by hydraulic pressures. With these constructions, the inclination angle of the swash plate 9, i.e., the theoretical discharge per revolution of the conventional pump, can be varied or adjusted.
There arises a case where the relatively complicated and expensive input shutting-off mechanism should be removed in order to reduce the weight of the hydraulic operation system equipped with the conventional pump and to simplify the construction thereof. Even if the input shutting-off mechanism is removed, there arises no drawback as far as a normal load is applied to the driving shaft 4 of the conventional pump.
However, in the case that worn particles, or the like, intrude in a discharge passage, or the like, and they block the discharge passage, in the case that insufficient lubrication occurs and it results in the seizure at the sliding portions between the pistons 10 and the bores 7, between the end surfaces of the cylinder block 6 and the valve plate 11, and between the shoes 8 and the swash plate 9, there arise abnormal operations where high loads are applied to the driving shaft 4. Even when such abnormal operations happen, the driving shaft 4 is kept rotating forcibly by an engine, and eventually internal breakages occur.
In order to avoid this drawback, the conventional pump is provided with a relief valve so as to avoid the blocked discharge passage, or as set forth in Japanese Unexamined Utility Model Publication (KOKAI) No. 62-117,571, a compressor is provided with a locking sensor which is adapted to sense the seizure at the sliding portions. However, these counter measures result in substantially increasing manufacturing cost because the increasing discharge pressure, the increasing temperature, or the rotary or non-rotary state must be detected.